1. Field of the Invention
The present invention relates generally to a planarization apparatus, particularly to a planarization apparatus of a type that processes the reverse of a semiconductor wafer.
2. Description of Related Art
A planarization apparatus that grinds one face or the reverse, on which chips are not formed, of a semiconductor wafer includes a chuck for holding the wafer, a grinding wheel for rough grinding, a grinding wheel for a finishing grinding, a reverse face cleaning unit, and so forth. In the planarization apparatus, the other face or the obverse of the wafer is held by the chuck by suction, and the rough grinding wheel is pressed against the reverse, then the reverse is roughly ground by rotating the chuck and the grinding wheel. After that, the wafer that has been roughly ground is detached from the chuck. Then, the wafer is held by another chuck for the finishing grinding and is finely ground by the finishing grinding wheel. The wafer of which reverse has been finely ground is then transported to the reverse cleaning unit, and the reverse is cleaned. Thus, the grinding process for the reverse of one wafer by the planarization apparatus is completed.
The wafer for which the reverse face grinding has been completed is transferred to the next process, an etching process. The wafer is transported from the planarization apparatus to the etching unit, and is etched, so as to remove a broken layer (also called a spoiled layer or a damaged layer) which was formed on the reverse of the wafer during the reverse face grinding.
However, if the wafer is ground in the planarization apparatus to be extremely thin that is close to a finished product, the wafer is easily broken (cracked) when transporting the wafer from the planarization apparatus to the etching unit because the wafer is extremely thin and hence weak in view of strength, and also because of the broken layer formed on the reverse of the wafer.
In order to avoid this problem, the conventional planarization apparatus grinds the wafer in a thickness with which the wafer is not broken during the transportation. Describing the thickness of the wafer for example, a wafer is sliced in thickness of 725 xcexcm from an ingot. The wafer is then ground by the planarization apparatus in the thickness of 250 xcexcm in the rough grinding, and is further ground in the thickness of 200 xcexcm in the finishing grinding. Thereafter, the wafer is processed in the standardized thickness of 50 xcexcm by the last process, the etching process.
As described above, in order to prevent the breakage of the wafer during the transportation, the wafer cannot be processed close to the standardized thickness in the conventional planarization apparatus. Because of that, the removal amount in the etching process (150 xcexcm in the above example) must be large and the time for etching has to be long, thus the throughput cannot be improved.
The present invention has been developed in view of the above-described circumstances, and has as its object the provision of a planarization apparatus by which the throughput can be improved without breaking the workpiece.
In order to achieve the above-described objects, the present invention is directed to a planarization apparatus, comprising: a holding device which holds a workpiece; a grinding device comprising a grinding wheel which grinds a face of the workpiece held by the holding device; and an etching device which etches the workpiece.
As the holding device, the following devices can be used such as: a device which holds the workpiece by suction, a device which freezes and holds the workpiece through an ice film, a device which holds the workpiece with static electricity, a device which holds the workpiece with an adhesive sheet, a device which holds the workpiece with a friction force, and a device on which the workpiece is simply placed.
According to the present invention, since the etching device is installed in the planarization apparatus including the grinding device, the grinding and etching of the wafer can be performed in the same apparatus. Thus in the present invention, the workpiece does not have to be transported from the planarization apparatus to a separate etching apparatus, so that the workpiece can be ground by the grinding device in the thickness close to the standardized thickness. The throughput can be therefore improved.
Preferably, the planarization apparatus further comprises a moving device which moves the holding device between a grinding position of the grinding device and an etching position of the etching device, and the workpiece is ground by the grinding device and etched by the etching device while keeping held by the holding device.
According to the present invention, the planarization apparatus can precisely process the workpiece without breaking the workpiece because the workpiece is ground and etched while keeping held by the holding device. In contrast, the conventional apparatus transfers the workpiece from a holding device that is exclusively used for the grinding device to another holding device that is exclusively used for the etching, and the problem hence occurs in that the workpiece may be broken by an external force when transferring the workpiece. The present invention can eliminate this problem.
Preferably, the etching device etches a broken layer formed on the face of the workpiece having been ground by the grinding device, and/or the etching device etches the face of the workpiece by an amount of thickness variation of the workpiece. Thereby, a precisely-processed workpiece can be obtained.
Moreover, a plurality of holding devices are provided, and the holding devices are moved from the grinding position to the etching position in an order. Thus, the grinding and etching can be performed at the same time, and the net working rate is improved compared with the case in which the workpiece is ground and etched with one holding device.
The holding device is detachably connected with a spindle, and the holding device can independently be moved by detaching the holding device from the spindle whenever the moving device moves the holding device. Therefore, the workload on the moving device can be reduced, and only the spindles that are suitable for the respective processes are necessary. Hence, the manufacturing cost of the apparatus can be low.
Further, the etching device is installed in the planarization apparatus including a rough grinding device and a finishing grinding device. Hence, the successive process from the rough grinding, the finishing grinding through the etching can be performed by only one planarization apparatus. In addition, the moving device is provided for moving the holding device for the workpiece to the rough grinding position, the finishing grinding position, and the etching position; thus, the entire process can efficiently work without dropping the net working rate even though the construction is such that the single or plural rough grinding device, the single or plural finishing grinding device, and the single or plural etching device are arranged in combinations.
In the planarization apparatus according to the present invention, the holding device is transferred toward the etching vessel by the transferring device so that the workpiece is housed in the etching vessel while the holding device keeps holding the workpiece. Then, the etching solution is projected from a nozzle to the workpiece to etch the workpiece. Therefore, the workpiece can be precisely processed without breakage.
The planarization method according to the present invention is applied to the planarization apparatus comprising the grinding device and the etching device. The etching device etches the workpiece by an amount more than a removal amount required for removing the broken layer formed by the finishing grinding, calculated by doubling a standard deviation, and less than a larger value between a removal amount required for correcting an unevenness of a thickness during the finishing grinding and removing the broken layer, calculated by sextupling a standard deviation, and 20 xcexcm. This enables the removal of the broken layer formed by the finishing grinding without lowering the rate of operation.
Further, the planarization method according to the present invention is applied to the planarization apparatus comprising a rough grinding device, a finishing grinding device and the etching device. The finishing grinding device finely grinds the workpiece by an amount more than an amount required for removing the broken layer formed by the rough grinding, calculated by doubling a standard deviation, and less than a larger value between a removal amount required for correcting an unevenness of a thickness during the rough grinding and removing the broken layer, calculated by sextupling a standard deviation, and 150 xcexcm. This enables the removal of the broken layer formed by the rough grinding without lowering the rate of operation.
Furthermore, the planarization apparatus according to the present invention comprises a sensor which measures the thickness of the workpiece, and the thickness of the workpiece is measured before and/or during the process so that the grinding amount and/or the etching amount can be controlled in accordance with the measured value; thus the wafer can be processed with a desired thickness.